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IRON

173

the manganese to permanganic acid and comparing the colour of the
solution with that of a permanganate solution of known titre.1

Preparation of the control solution 2 : 0-072 gram of 'chemically pure
potassium permanganate is dissolved in water and the volume made up
exactly to 500 c.c. ; i c.c. of this solution corresponds with 0-05 m. grm.
of manganese.

Procedure. 0-2 gram of the metal is dissolved in the hot in 15-20 c.c.
of nitric acid (D 1-2) in a 100 c.c. measuring flask, the liquid being after-
wards heated to boiling to expel nitrous fumes, cooled, made up to volume
and mixed.

Four portions, each of 10 c.c., are pipetted into four beakers of about
75 c.c. capacity, 2 c.c. of nitric acid (D 1-2) being added to each beaker.
The first portion is heated over a small flame to boiling, the beaker being
covered with a clock-glass meanwhile. The cover is then quickly removed,
about 0-5 gram of lead peroxide free from manganese added to the boiling
liquid and gentle boiling maintained for two minutes longer.

When cold, the liquid is filtered by decantation  care being taken that
no lead peroxide passes  through a small asbestos (this being ignited, and
washed with permanganate solution and then with water) filter, the nitrate
being collected in an Eggertz tube (see Fig. 12, p. 170) and the residual
lead peroxide and the filter washed with about 5 c.c. of water until the
wash water passes through colourless. The solution in the Eggertz tube,
when shaken, is ready for the colorimetric observation.

The other three portions are treated in the same way, the nitrations
being effected with the same filter and the liquids collected in Eggertz tubes
to serve for confirmatory purposes.

The colorimetric comparison is made by pipetting into another Eggertz
tube 1-4 c.c. of the control permanganate solution according to the colour
intensity of the other tubes, and diluting carefully with water until an exact
match is obtained.

If the volume of the solution from the sample of steel is v and I c.c. of
the control solution has to be diluted to V c.c. to give the same depth of
colour, the percentage of manganese in the sample will be

v X 0-05

This rapid and fairly accurate method cannot be applied to materials con-
taining more than 1-1-5% f manganese.

4.  Determination of the Phosphorus

Many methods are in use for the determination of phosphorus in ferrous
products, those most generally employed being based on the conversion
of the phosphorus into phosphoric acid and precipitation of the latter with
ammonium molybdate. The ammonium phosphomolybdate separated
may be determined gravimetrically, volumetrically, densimetrically, etc.
Descriptions will be given here of Finkener's gravimetric method, which

1  Some prefer to make the comparison with a steel of known manganese content.

2  This solution, stored in the dark, keeps for about three weeks., oxidising